fix(tests): update getShares assertions to match C3 fixture cleanup

SharesTests expected the old demo.navidrome.org URL and "demo" username
that were replaced in commit b3b0820. Update the two assertions to match
the fixture values: music.example.com and "alice".

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: MathieuDubart

Tests/swiftsonicTests/SharesTests.swift

@@ -30,9 +30,9 @@ struct GetSharesTests {
 
         let first = try #require(shares.first)
         #expect(first.id == "sh-abc123")
-        #expect(first.url == "https://demo.navidrome.org/share/sh-abc123")
+        #expect(first.url == "https://music.example.com/share/sh-abc123")
         #expect(first.description == "NIN collection")
-        #expect(first.username == "demo")
+        #expect(first.username == "alice")
         #expect(first.visitCount == 3)
         #expect(first.expires != nil)